Abstract A historical description of Wallace H. Coulter's invention and development of his companies' instrumentation for analysis of blood cells or particles has never been available, and too often, this void has been addressed by conjectural or promotional publications. A history thesis, based on the author's access to Coulter's personal papers and to files kept by his father, Joseph R. Coulter, Sr., has recently become available; for the first time Coulter's developmental process is factually detailed against the historical context in which it occurred. This paper is an introductory overview of that developmental process as discussed therein. It should be of interest to not only the ISAC membership, but to Cytometry's broader readership as well.